Temper Tantrum in classroom, what do I do?

My 7 year old son's teacher came back from maternity leave two months ago, ever since then it's been hell. He really misses his substitute. He has a meltdown almost everyday (mostly in the noontime). When he is in time out or receives a warning, he goes beserk cuz he knows that I'm going to ground him too. He never use to behave like that in pre k or kindergarten or even earlier this year.

Part of the problem too is that he knows that we are moving soon (next month) because his dad is in the service. You'd think after 7 years, he'd be use to it by now but I guess a child will never be use to moving especially when they're older.

Anyway, things gotten so bad (him kicking teacher, throwing down chairs/desk/books, etc) that the principal has been called in. He gets in trouble in his other classes with other teachers too. The school is pretty fed up and is about to suspend him. Now they want me to pick him up at 1 pm everyday since his meltdown is around that time frame. I don't know what to do...ugh!!!!